An electrochromic device may include a working electrode that includes a high temperature stable material and nanoparticles of an active core material, a counter electrode, and an electrolyte deposited between the working electrode and the counter electrode. The high temperature stable material may prevent fusing of the nanoparticles of the active core material at temperatures up to 700° C. The high temperature stable material may include tantalum oxide. The high temperature stable material may form a spherical shell or a matrix around the nanoparticles of the active core material. A method of forming an electrochromic device may include depositing a working electrode onto a first substrate, in which the working electrode comprises a high temperature stable material and nanoparticles of an active core material, and heat tempering the working electrode and the first substrate.